When a document image, such as a scanned page, is processed, the document image acquired by an image input equipment such as a scanner or a camera may be rotated relative to its actual orientation, for example, by an angle of 90°, 180° or 270°. Therefore, it is necessary to recognize the orientation of the document image. Examples of the method for recognizing the orientation of the document image are given in the following literatures:
Ranjith Unnikrishnan, “Combined Script and Page Orientation Estimation using the Tesseract OCR engine”, ICDAR2009;
Xin Wan, “Method for correcting text image”, CN 101833648 A; and
Zhigang Fan, “Page orientation detection based on selective character recognition”, US 2009/0274392 A1.